Are sugars and starches dangerous for rabbits?

A current trend in the rabbit world is to believe that sugars and starches are dangerous for rabbits and that any food that contains sugars and starches should be avoided. In reality, this would mean avoiding all plants because they all contain sugars and starches. Photosynthesis is the chemical process that takes place in the leaves of green plants. The green pigment, chlorophyll, utilises energy from sunlight to convert carbon dioxide and water into glucose and oxygen. Glucose is then converted into other sugars and starches that are present in all parts of the plant and can be stored in the roots

Fruit and root vegetables are the foods that have a reputation for being dangerous because of their sugar content. It is true that they are sweet and the starch content of some root vegetables is higher than in the leaves. However, these foods are not 'dangerous', although they are fattening and nutritionally unbalanced. Rabbits enjoy eating fruit and root vegetables which do not need to be excluded from the diet and can be fed in moderation to slim rabbits. They need to be excluded from the diet of rabbits that are overweight. 

Nuggets and pellets are not free from sugars and starches. Examination of the composition of pellets and nuggets (on the side of the packet) show that they often contain starches in the form of wheat, oats, soya beans or peas. Some incorporate molasses, which is a sweet by product of sugar refining. 

What are the perceived dangers of sugars and starches?

On many websites and information leaflets about feeding rabbits, serious stomach upsets, diarrhoea and 'soft stools' are the conditions that are associated with sugars and starches in the diet. These are often attribute to 'caecal dysbiosis', which is not a condition that is documented in the scientific literature about rabbit diseases. 'Caecal dysbiosis’ means a disruption in the balance of micro-organisms in the caecum, and does occur in enterotoxaemia, which is a sudden, serious, and usually fatal disease in rabbits. Enterotoxaemia does not cause soft caecotrophs that stick to the fur under the tail. However, there is a theory (see below) that dietary starch is linked with enterotoxaemia, which may be the reason why some people think sugars and starches are dangerous for rabbits. 

Carbohydrate overload theory

The carbohydrate overload theory is based on the bacteria,  Clostridium spiriforme,  that is often  found in outbreaks of enterotoxaemia in rabbit colonies. This bacterium requires glucose for toxin production. The  idea of the carbohydrate overload theory is that a diet that is high in starch provides glucose to the caecal microflora for toxin production and this results in enterotoxaemia. Even in the scientific community of commercial rabbit nutrition, this theory is not universally accepted and even if it were true, it would only apply to young rabbits with an undeveloped caecal microflora. In adult rabbits, sugars and starches are absorbed in the small intestine. A high carbohydrate diet tends to be low in fibre and this is more likely to be the reason that commercial rabbits are so susceptible to enteric disease. They also live in crowded conditions where they are stressed and exposed to high envoronmental loads of bacteria and other microorganisms, such as coccidian, that can also cause enteritis. 

Carbohydrates and pet rabbits

In contrast to commercial rabbits, pet rabbits are usually adults that live on their own, in pairs or in small groups. Crowded, insanitary conditions are unusual  Unlike commercial rabbits, they are not exposed to enteric infections from other rabbits or from a contaminated environment.  Enterotoxaemia is rare despite the fact that most pet rabbits are fed on a diet that contains starches. A look at the ingredients of muesli mixes, nuggets or pellets will show that they contain oats or wheat i.e carbohydrates. Some contain sugary molasses.  Common sense would say that  sugary, starchy foods are highly unlikely to kill an adult pet rabbit by upsetting its caecal microflora otherwise there would be a lot of dead pet rabbits about. The rabbits that live on muesli mix and honey flavoured treats from the pet shop do not die from enterotoxaemia. They suffer from obesity instead. High calorie treats and muesli mix are never a good idea for rabbits.  Unfortunately, some rabbit food manufacturers still produce and market them

Soft caecotrophs

Starchy or sugary foods are often blamed for soft faeces that can stick to the fur under the tail. This is often interpreted as diarrhoea but it is really caecotrophs that have not been eaten by the rabbit. There are many reasons for rabbits to leave their caecotrophs uneaten and if the rabbit consumed them, the consistency of the caecotrophs would be unknown. Common reasons for rabbits to not eat their caecotrophs include fat rabbits or those with arthritis or spinal problems that make it difficult to reach under their tail to eat their caecotrophs and keep themselves clean. Studies have shown that dietary starch has no influence on the chemical composition of caecal contents or on the production or composition of soft and hard faeces. Any link between high carbohydrate diets and soft caecotrophs is probably due to the indirect relationship of carbohydrate with fibre. High carbohydrate foods (such as fruit and cereals) tend to be low in indigestible fibre. The fibre content of caecotrophs affects their consistency, more fibre makes making them firmer. This is why a high fibre diet is a good remedy for soft caecotrophs. A high fibre diet is less fattening, so the rabbit is thinner and more able to reach round to consume the caecotrophs.  The rabbit will be hungrier and keener to eat caecotrophs.